The elephant has a secret hidden right up its nose.
Its famously muscled, boneless trunk can move in a virtually infinite number of directions and is capable of performing a variety of tasks, such as plucking leaves and vacuuming up water and snacks. These skills have inspired nature lovers as well as engineers who work building robots capable of similar feats of flexibility and strength.
But the trunk is more than just muscle, and the abilities of this appendage may also depend on something obvious but often overlooked: the skin.
In a study published last Monday (18) in The Proceedings of the National Academy of Sciences, researchers report that, due to important differences in the flexibility of the skin in the different areas of the elephant’s trunk, it extends more in the upper part of the trunk. outward than at the bottom, closer to the mouth.
The trunk is “a muscular multitool that can do all these things, but one of the tools in your pocket is different skins,” said Andrew Schulz, a doctoral student in mechanical engineering at the Georgia Institute of Technology and an author of the new study. .
As part of an ongoing collaboration with the Atlanta Zoo, Schulz and his colleagues challenged two African elephants — a male and a female — to horizontally stretch their trunks to pick up food placed far away.
The simplicity of this reaching movement reveals the complexity of what the trunk needs to do.
When viewed on a high-speed camera, the elephant’s trunk does not extend evenly like other muscular appendages such as an octopus’ arms or a human tongue. Instead, it unfolds outward like a telescope, with the tip extending first, followed by the front half of the trunk.
The researchers hypothesize that this telescopic behavior might be more energy efficient than moving the entire trunk. If it were split into pieces, there is about 1 liter of muscle at the tip, but a whopping 22 liters of muscle at the base, which would be heavy and energy intensive if the movement were more uniform.
With even more detailed analysis, the researchers noticed “strange asymmetries popping up everywhere, as if things were different at the top and bottom,” Schulz said. As the elephant’s trunk lengthened, the outward-facing half extended 15% more than the ground-facing half.
“I still remember I literally ran into my counselor’s office like an idiot holding up the laptop to show him some of the results, because it was all so amazing,” Schulz said.
Initially, the researchers thought this top-down difference in proboscis length was a mistake, but later mechanical testing cleared up any doubts.
When they stretched skin samples taken from the frozen trunk of an elephant that died in a zoo, the researchers found that the skin on top, with its long folds, was 15% more flexible than the wrinkled skin below the trunk.
These characteristics correspond to the different functions that the skin offers. The upper surface of an elephant’s trunk needs protection from the sun and other animals, and it has this “flexible armor like Kevlar, with deep folds that are very, very easily stretchable,” Schulz said. On the other hand, the lower part of the trunk is covered by smaller wrinkles and is used for holding and moving objects, but it rarely sees sunlight.
The new study is a good reminder of the “involvement of the skin in biomechanics,” said Michel Milinkovitch, a professor at the University of Geneva (Switzerland) who has conducted research into the biomechanical complexity of elephant trunks.
For engineers who take inspiration from elephants, it’s essential to realize that they shouldn’t just focus on their robots’ engines and other internals, but also think about “playing with the geometry of the envelope,” said Milinkovitch, who was not involved in the study. . “No one has yet incorporated this into real robots,” he added.
The research uncovers new possibilities for future robots to more accurately mimic the powers of the elephant’s trunk, and also underscores the importance of conserving endangered species that know how to wield these marvelous instruments.
“Bioinspiration is great as long as the animals we’re taking bioinspiration from exist,” Schulz said.
Translated by Luiz Roberto M. Gonçalves
